Assessment of influence of facemask treatment with skeletal anchorage on the temporomandibular joint using magnetic resonance imaging: a preliminary study

ABSTRACT Objective: The aim of the study was to investigate the influence of facemask treatment with skeletal anchorage on the temporomandibular joint (TMJ) using magnetic resonance imaging (MRI), in patients with Class III malocclusion, accompanied by maxillary retrusion. Methods: Fifteen patients with a mean age of 12.1±1.43 years were included in the study. All patients were treated using facemask with skeletal anchorage after eight weeks of Alternate Rapid Maxillary Expansion and Constriction (Alt-RAMEC) protocol. Magnetic resonance imaging was performed before and immediately after facemask treatment for TMJ evaluation. Disc position, condylar translation, degenerative changes of the condyles, and joint effusion were evaluated. To assess whether the alterations associated with the treatment were statistically significant, McNemar and marginal homogeneity tests were used. Results: After facemask treatment, a statistically significant change was observed in the disc position (an anterior disc displacement with/without reduction in five TMJs) (p<0.05). The alteration in the condylar translation was not statistically significant (p>0.05). This treatment did not cause degenerative changes of the condyles or effusion in any of the TMJs. Conclusion: Facemask treatment with skeletal anchorage following the Alt-RAMEC protocol had a minimal influence on the TMJ, only by means of disc position, which was not negligible. Long-term results of such treatment are required for following up the changes observed in the TMJs.


INTRODUCTION
The purpose of the facemask treatment is to redirect or stimulate the growth of the maxilla forward, in patients with Class III malocclusion accompanied by maxillary retrusion. To increase its efficiency, the facemask has been applied in conjunction with rapid maxillary expansion (RME) and, recently, with the Alternate Rapid Maxillary Expansion and Constriction (Alt-RAMEC) protocol. However, some dental compensations (maxillary incisor proclination) were observed with these treatment protocols. 1,2 Thus, a more rigid anchorage was used for a pure orthopedic forward movement of the maxilla, providing more stable results. 3 Finally, facemask treatment with skeletal anchorage following the Alt-RAMEC protocol was applied to further increase the skeletal effect in severe cases and also to achieve skeletal effects for patients in the late treatment period. 4 The conventional type of facemasks used for redirecting or stimulating the growth of the maxilla forward often obtains support from both the forehead and chin, and heavy forces are applied with these appliances for orthopedic effect. Grandori et al. 5 reported that 75% of the force produced by the facemask is transmitted to the temporomandibular joint (TMJ). Any force transmitted to the TMJ may have an impact on TMJ components.
In this situation, the risks of facemask treatment include posterior displacement of the condyle and anterior displacement of the articular disc, which may cause temporomandibular disorder (TMD); however, informations on this issue are controversial. Ricketts 6 revealed that facemask treatment used for achieving a more normal association between the maxilla and mandible might promote TMD due to the force transmitted to the TMJ in the posterior direction. Contrarily, in a systematic review study recently published by Huang et al., 7 it was concluded that facemask treatment led to the displacement of the condyle, but presented evidence supporting the morphological adaptation of the TMJ to a changing functional status and that it might not be a risk factor for the development of TMD.
The influence of facemask treatment on the TMJ has been evaluated using various methods, such as two-dimensional cephalogram, computed tomography (CT), cone beam computed tomography (CBCT), thin-plate spline analysis, mandibular position indicator, and Research Diagnostic Criteria for Temporomandibular Disorders. [8][9][10][11][12][13][14] However, in the literature, a study assessing the influence of facemask treatment on the TMJ using magnetic resonance imaging (MRI) has not been conducted yet, except for a thesis study. 15 It is well-known that MRI is the best imaging method that allows the examination of the soft tissues of the TMJ. Additionally, MRI has been shown to have a high accuracy rate in evaluating the osseous changes of the TMJ. 16 Therefore, this study specifically aimed to investigate the MRI alterations in the TMJs of patients with skeletal Class III malocclusion accompanied by maxillary retrusion who underwent a facemask treatment with skeletal anchorage after the Alt-RAMEC protocol.

MATERIAL AND METHODS
The present study was approved by the local ethics committee (approval number: LUT 06/91-20). Patients and their parents were informed about the treatment in detail, and written informed consent forms were obtained from the parents who agreed to participate in the study.
According to the result of power analysis, a sample size of 28 TMJs would achieve 81.377% power at a significance level of 0.050 using a one-sided non-inferiority test of correlated proportions when the standard proportion is 0.070. The maximum allowable difference between these proportions that still results in non-inferiority (the range of non-inferiority) is 0.120, and the actual difference of the proportions is 0.000. of TMD such as joint sounds, limited mouth opening, mandibular shift, difficulty in chewing, and pain. Initial skeletal sagittal relationships of the patients in terms of ANB angle and Wits appraisal were -1.3±1.76° and -7.1±3.09mm, respectively.
All patients were treated with Delaire-type facemask with miniplate anchorage (Multipurpose Implant; Tasarimmed, İstanbul, Turkey) bilaterally inserted on the lateral nasal wall of the maxilla, following eight weeks of Alt-RAMEC protocol with bonded RME appliance (Fig 1). Alt-RAMEC protocol began with expansion, followed by final constriction (considering that maxillary expansion was not required). The time for each expansion or constriction course was two weeks, and the daily activation of the screw for each course was 0.5 mm a day.      The impact of facemask treatment on the TMJ has been evaluated clinically and radiologically. 8,9,12,14,15 Although clinical evaluation helps in establishing the diagnosis of TMD, it may not provide sufficient information for the overall diagnosis. Accordingly, the clinical evaluation of the TMJ should be supported with radiological examination. In facemask studies, researchers often used two-dimensional cephalograms for the radiological evaluation of the TMJ. 8,10,14 Subsequently, they preferred more advanced methods such as CT and CBCT for a more detailed evaluation. 7,9 To date, a study assessing the alterations in TMJs using MRIs in patients with Class III malocclusion treated via a conventional facemask or a facemask with skeletal anchorage following the Alt-RAMEC protocol has not been conducted yet. MRI is a relatively reliable method used to assess the TMJ. It was reported that the accuracy rate of MRI was 95% in evaluating the position of the disc and the soft tissue around it. Moreover, MRI has been reported to be 93% accurate in evaluating the osseous alterations of the TMJ. 16 Since it has no radiation side effects, it is considered superior compared to other advanced imaging methods such as CT and CBCT. This advantage of MRI is specifically important for children whose growth and development period continue.
However, MRI is expensive for routine clinical use.
In the present study, only patients with no clinical symptoms of TMD were included, but MRI examinations of 2 TMJs (in one patient) indicated an anterior disc displacement with reduction before the facemask treatment. This finding was consistent with the findings of a previous study showing that an anterior disc displacement could be detected in the radiological examination of symmetric or asymmetric patients with Class III malocclusion and without clinical symptoms of TMJ . 19 There could be some reasons for this situation. First, a disc displacement with reduction can remain asymptomatic for a long time, due to the adaptive physiological processes that may occur. The primary adaptive physiological process is the retrodiscal fibrosis, which can explain why the patients having disc displacement with reduction feel no pain. Another reason could be the change in the morphology of the condylar head resulting from remodeling. In addition, it is possible that the neo-neuromuscular system will balance out the desired occlusion, keeping the condyle in its physiologic position, and prompting accomplishment of a normal disc position. The same 2 TMJs also had a bilateral joint effusion. Another TMJ had a unilateral restricted condylar translation. Despite the studies showing that there might be an association between TMD and Class III malocclusion, 20,21 TMD was not detected in most of the TMJs in the present study, except for these 3 TMJs.
Potential causes of TMJ alterations after facemask treatment include the force produced by the facemask, forward movement of the maxilla, posterior displacement of the condyle, and growth. Among these, the force produced by the facemask is the primary factor. A large part of this force is transmitted to the TMJ. 5 It was reported that the stress levels created on the TMJ by orthopedic forces were smaller than those during normal clenching and chewing functions and therefore would not damage the TMJ. 22,23 Even so, its effect on the TMJ was investigated by several researchers because facemask was hypothesized to create a different vector in the TMJ from the vector occurring In the present study, it was observed that the restricted translation of 1 condyle improved with facemask treatment, but a condyle with preexisting normal translation had a restricted movement after facemask treatment. This may be caused by a real restriction in condylar translation, or by the patient not fully opening the mouth.
Applying force to the TMJ using the Delaire-type facemask leads to compressive movement of the condyle through the glenoid fossa in the posterior direction. 11 As a result, a degenerative change on the condyle can be expected. In animal studies, after retraction forces, it was shown that the remodeling process of the condyle was altered, and a resorption was observed at the posterior surface of the condyle. 25 With facemask treatment, no degenerative changes of the condyles were detected in the present study. The absence of degeneration on the condyle can be attributed to the condyle's morphological adaptation mechanism, as patients continue to grow and develop, and the condyle is still under modification and significantly varies. 26 It was also demonstrated that the increase in occlusal vertical dimension obtained by the installation of dental appliances promoted the thickness of condylar cartilage. 27 In addition to growth, the application of the facemask over bonded RME appliance may be another factor compensating for the resorption that may occur on the condyle.
TMJ effusion is a condition characterized by an excessive collection of intra-articular synovial fluid that can be easily diagnosed on MRI examination. No effusion was detected in 95% of patients having normal disc position. 28 However, it could be frequently observed in asymptomatic or symptomatic patients with TMD. 29,30 In this study, effusion was not observed in any of the TMJs having normal/abnormal disc position, either before or after treatment, except for 2 TMJs of 1 patient. It has been reported that the severity of effusion increases in patients with anterior disc displacement. 31 The aforesaid 2 TMJs of 1 patient also had a bilateral anterior disc displacement with reduction. Although an orthopedic force was applied to the TMJs, the severity of effusion in this patient did not increase. In fact, discussions regarding the association between anterior disc displacement and joint effusion are still ongoing, and no definitive conclusion has yet been reached because joint effusion was not diagnosed in some of the patients having anterior disc displacement. 30 The absence of joint effusion in 5 TMJs having an anterior disc displacement after maxillary protraction